Dolphin is the buzzword in Melbourne after Michael Phelps blitzed his way a record seven gold medals at swimming's World Championships.

But we're not talking about marine mammals here. The 21-year-old superstar has refined a technique called the "dolphin kick" and he used it to devastating effect to take yards out of his opponents at the start and at turns.

WHAT IS IT?

The dolphin kick has helped Michael Phelps to further world records

Emulating the way a dolphin cuts through the water with its flipper, the dolphin kick replaces a standard underwater leg kick with an explosive whipping motion, which runs along the legs from hips to toes minimising water resistance.

It is a very tricky movement to perfect. Done wrong, the dolphin stroke will have a detrimental impact, but timed right it can provide a surge through the water worth half a body length's advantage on every turn.

Phelps uses the kick when he is under water, so he gets to perform the kick once for every length he does. This happens:

Immediately after diving in at the start before settling into a standard stroke

Immediately after a turn before returning to the surface to resume a standard stroke

HOW DID IT COME ABOUT?

Phelps brought the dolphin kick back into the spotlight, but the technique was honed in the 1980s by fellow American David Berkoff, Japan's Daichi Suzuki and by Puerto Rican Jesse Vassalo.

Feeding off each other, the three swimmers are credited with evolving an alternative sub-marine kick so efficient that a massive advantage could be gained by staying under water for much of the race.

By 1988, "Berkoff's Blastoff" - as it was dubbed - was so potent that he broke the 100m backstroke world record in the heats of the Seoul Olympics. But Suzuki hit back in the final and was the surprise winner as the pair swam roughly half the race under water, eclipsing the rest of the field.

Their staggering results prompted rivals to copy them and Fina, swimming's governing body, to impose a rule that limits a swimmer staying completely submerged to only 15m at the start and an additional 15m after every turn.

Backed up by a research project into fluid dynamics at George Washington University, Phelps and the US swim team have further refined the dolphin kick to make it explosively effective within Fina's 15m underwater allowance.

DOES IT ACTUALLY WORK?

You bet it does. Phelps smashed five world records in Melbourne and might well have had an eighth gold medal for his growing stash had the USA not been disqualified in the medley relay.

Britain's head coach Bill Sweetenham believes the dolphin kick's impact is so great that it deserves to be called a swimming stroke in its own right.

PHELPS' SEVEN WORLD GOLDS

200m freestyle WR

100m butterfly

200m butterfly WR

200m ind medley WR

400m ind medley WR

4x100m freestyle relay

4x200m freestyle relay WR

"The world has been delivered a huge lesson in skills by the Americans like we've never seen before," he told Swim News.

"The dolphin kick we're seeing has to be considered the fifth stroke now. I think swimming has moved to a new era, a new level. It will challenge all coaches and swimmers around the world.

"We're seeing things we would not normally expect to see, but the world will respond, including us."

But BBC commentator and former Olympic medallist Sharron Davies is not sure an effective response will be possible because the Americans are always pushing the boundaries.

"I don't think Britain has the resources or the depth to do what the Americans can do," she said.

"What the Americans have been doing is a lot of research into dolphin movements and they basically worked out that you can go a lot quicker under water doing the dolphin kick on your turns and your starts.

"They have been doing all this special research and they have not let the cat out of the bag much. But it is something the rest of the world will be working on between now and next year."

With Phelps shattering four individual world records in Melbourne, taking up to two seconds off some times, there will a lot of hard work between now and the Olympics in Beijing next year.